The present invention relates to a method and a device for controlling the accuracy of the movement of a unit which moves on slides, such as a table moving on hydro or air static slides.
Every solid unit moving in a linear direction has the potential to make five independent types of errors which are defined by the accuracy of the slides on which the unit moves and these errors depend on the movement""s coordinate.
If a unit is moving in the Z direction (see FIG. 1), there are five possible components of deviation from the ideal straight motion. They are:
xcex94x(z)xe2x80x94linear deviation in x-direction;
xcex94y(z)xe2x80x94linear deviation in y-direction;
xcex94xcex1(z)xe2x80x94angle deviation when the unit rotates around the axis x;
xcex94xcex2(z)xe2x80x94angle deviation when the unit rotates around the axis y;
xcex94xcex3(z)xe2x80x94angle deviation when the unit rotates around the axis Z.
U.S. Pat. No. 4,653,408 shows one way to control the attitude of a table that is moving on hydrostatic slides. The main defects of this way are (a) it is possible to compensate only the attitudes of linear deviation and (b) the compensation of linear deviations will change the uncontrolled angle deviations.
It is proposed herein to provide a simple method and device for the simultaneous and independent compensation for all five possible error components. This method can be used both for special designed new slides and for correcting the movement of existing slides.
Because five independent components of the total error have to be controlled, the device of the present invention has five independent valves and every valve changes the flow of a fluid, such as oil or air, independently from the other valves. The valves are connected to the recesses and the commutations between the recesses in such a way that every valve is responsible only for compensation of one component of the total error and a change of flow through a respective valve will not be an influence on the four other components of the total error.
The method of the present invention very easily improves the accuracy of a moving unit, such as a table, which moves on slides. The method involves measuring, one by one, all five components of the total error or five independent functions of these components and after every measurement adjusting each valve that is responsible for each respective component of the total error until the error is eliminated. As previously discussed, the adjustment of each valve is independent from the adjustments for the other four valves. Using the method of the present invention, if some independent units are moving in linear directions, the same method can be used both to make the movements really straight and to achieve the required accuracy for the angles between the directions of the unit""s movements.
The only alternative to the method of the present invention is the hand scrapping of slides according to measurements of a table""s movement. Hand scrapping is widely used for all types of high precision and ultra precision machine tools and for three-coordinate measuring machines as well. The method of the present invention is much cheaper, shorter, and more accurate compared with the hand scrapping of the slides. Additionally, it allows one to correct the movement""s accuracy directly in the customer""s shop after a machine is finally installed in a steady position.
Other details of the method and device of the present invention, as well as other advantages and objects attendant thereto, will become more apparent from the following detailed description and the accompanying drawings, wherein like reference numerals depict like elements.